code: def test_detect_variables_with_na_in_variables_entered_by_user(df_na):
      imputer = DropMissingData(
          missing_only=True, variables=["City", "Studies", "Age", "dob"]
      )
      X_transformed = imputer.fit_transform(df_na)
      assert imputer.variables == ["City", "Studies", "Age", "dob"]
      assert imputer.variables_ == ["City", "Studies", "Age"]
      assert X_transformed.shape == (6, 6)
  
file_path: feature_engine/tests/test_imputation/test_drop_missing_data.py
imports: import pytest
  from feature_engine.imputation import DropMissingData
label_desc: Use image node_id 3 for calling a global function with example usage: test_detect_variables_with_na_in_variables_entered_by_user(df_na) without return types